JPS5849603A - Purification of coke oven gas - Google Patents

Abstract

PURPOSE:In the production of hydrogen gas through the molecular sieve process, the procedure for forming gummy substances and removing them, that for extracting aromatic substances and removing them, and that for hydrogenating molecular oxygen and olefins and removing them are sequentially connected to obtain high-purity hydrogen gas. CONSTITUTION:Coke-oven gas F is introduced into the pressurizing process 1 where it is pressurized over 8 atmospheric pressure and gummy substances are formed, as the gas temperature rises. The gummy substances are removed by washing in the degumming process 2. The gas is introduced into the aromatics extraction process where trace amounts of aromatics such as BTX fractions and tars in the gas are removed by use of an aromatics extracting oil. The resultant gas is introduced into the hydrogenation process 4 where molecular oxygen and olefins are hydrogenated in the presence of a catalyst and removed. The coke oven gas, resultantly free from impurities, is introduced into the molecular sieve process 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-purity hydrogen gas from coke oven gas, and more specifically to a method for producing high-purity hydrogen gas from coke oven gas by a molecular sieve method. Regarding purification methods.

High-purity hydrogen gas is used in many fields of the chemical industry, such as hydrogenation of oils and fats, production of hydrogen peroxide, production of semiconductors, and hydrogenation and reduction of organic and inorganic compounds. on the other hand,
Coal carbonization coke oven gas is generated in large quantities and contains nearly 60% hydrogen gas, so if this hydrogen gas could be recovered in an economical way, it would be extremely beneficial for the chemical industry. It can be said.

Conventionally, as a method for producing hydrogen gas from coke oven gas, a cryogenic separation method has been used as a hydrogen residue for ammonia and methanol synthesis, but this method requires relatively large volumes (tens of thousands of Nm5A) of hydrogen gas. Although it is suitable as a production method, the equipment cost is high, the electricity cost for the gas compressor is high, etc., so the medium capacity (several thousand N rn ” /H) is not suitable.

In addition, there is a palladium diffusion method as a recovery method for high-purity hydrogen gas, but this method has the high cost of palladium;
Medium capacity (
Even though it is suitable for several hundred NmV'H), it is no longer suitable for medium capacity applications such as those mentioned above. One of the methods currently used for producing medium-capacity hydrogen gas is the reduced pressure regeneration type molecular sieve method. In this method, components other than hydrogen are selectively adsorbed and removed under pressure using a mixture of adsorbents suitable for each component to be removed in a mixed gas containing hydrogen residue to be treated, thereby obtaining high-purity hydrogen gas. Since the regeneration of the agent is simply carried out under reduced pressure, it requires few utilities and is an energy-saving method, so it is a method that has been widely adopted recently.

However, since the adsorbent used in this molecular sieve method is a mixture of various organic and inorganic adsorbents, it is easily poisoned by organic polymer compounds, highly polar compounds, etc., and in some cases becomes difficult to regenerate. Therefore, it is desirable that the gas treated by the molecular sieve method does not contain these harmful components.

However, coke oven gas naturally contains many components other than hydrogen. In other words, after leaving the coke oven, coke oven gas obtained from steel plants, coke plants, city gas plants, etc., undergoes many processes such as cooling, tar removal, ammonia recovery, light oil recovery, naphthalene removal, and hydrogen sulfide removal. Since it is purified, various impurities are removed, but it still contains BTX components (components represented by benzene, toluene, and xylene), aromatic substances such as tar, gummy substances, fine particulate substances such as dust, and olefins. It contains a considerable amount of hydrocarbons (coke oven gas in the present invention means the above gases). All of these components are harmful components that impair the adsorption ability of the adsorbent used in the molecular sieve method, and must be removed in advance to below a permissible concentration.

Another important problem is that there is no oxygen in the coke oven gas.
．． However, it is difficult to selectively adsorb and remove oxygen from hydrogen gas using currently industrialized adsorbents for the molecular sieve method, and therefore the required purity of the product hydrogen gas is low. If this cannot be achieved with this oxygen, it is necessary to remove this oxygen in advance using a method such as a method.

The present invention has been made to solve the above problems, and when producing high-purity hydrogen gas by the molecular sieve method using coke oven gas, it is possible to eliminate harmful components or It provides the most appropriate method for removing impurities.

The configuration of the present invention will be explained below by showing a system diagram in the drawings.

In the figure, (1) is a pressure increase process, (2) is a degumming process,
(3) is a dearomatization process, (4) is a hydrogenation process, and (5) is a molecular sieve process, where the thick arrow (F) indicates the flow of coke oven gas to be treated, and the arrow (P) The mark indicates the product hydrogen gas, and the arrow ■ indicates the purge gas.

The present invention is characterized in that the above steps are arranged in the order shown in the drawings, and hydrogen in the coke oven gas is most effectively separated by pre-treating the coke oven gas in a row-like arrangement. It will be done.

That is, in the method of the present invention, in order to maintain the entire process under high pressure, the pressure increasing step (1) is first arranged, and then the temperature increase of the coke oven gas in the pressure increasing step (1) is effectively utilized. A degumming step (2) is provided to prevent troubles due to the formation of gummy substances in subsequent equipment and piping, and furthermore, after the degumming step (2), trace amounts of BTX and tar present in the coke oven gas are removed. A dearomatization step (3) is arranged to remove aromatic substances such as. Water is used to remove oxygen with the help of a catalyst from the residue after this process has gone through and the impurities that cause clogging in the packing in the column tank in the next hydrogenation process have been removed. Addition process (
4) is placed next. Finally, a molecular sieve step (5) is arranged to separate and extract product hydrogen gas (P) from the gas supplied from the hydrogenation step (4).

All of the above steps are operated under high pressure, and the last step is the molecular sieve step (5) to separate hydrogen by FC, so the pressure increase step (1), which is the first step, and the last The molecular sheep process (5), which is the process of Regarding these steps (hereinafter collectively referred to as intermediate steps), several arrangement methods can be considered.

However, if, for example, the dearomatization step (3) is placed first in the intermediate steps, the effect of increasing the temperature of the coke oven gas in the pressure increasing step (1) can be effectively achieved in the degumming step (2), which is placed afterwards. Moreover, even if the hydrogenation step (4) is placed first, it will not only be the same as above, but also
The gas is supplied to the hydrogenation step (4) in a state where the residual BTX content and aromatic substances such as tar have not been completely removed, which causes clogging of the hydrogenation catalyst and causes the catalyst to become exposed. It is poisonous and inconvenient.

Therefore, in the intermediate process (C), as mentioned above, the degumming process (2) is placed first, followed by the dearomatization process (3), thereby purifying the coke oven gas in advance. The method of the present invention is characterized in that the hydrogenation step (4) in which a clean gas is treated at the end is arranged in this order.

Hereinafter, each step arranged as above will be explained in more detail.

In the pressurization step (1), the raw coke oven gas (F') is pressurized by a reciprocating or centrifugal compressor. The pressure after increasing the pressure is desirably 8 atm or higher, and optimally around 15 atm. This pressure is comprehensively determined in consideration of the pressure required for operations such as adsorption and desorption in the molecular sheep process described below. Due to the adiabatic compression effect during pressure increase, the temperature of the gas becomes around 80°C, so this temperature is used to remove gummy substances in the next degumming step (2). The cause of the formation of gum is not clear, but it is said that No in the gas reacts with the coexisting oxygen and becomes NO2, which reacts with diolefins with conjugated double bonds present in coke oven gas and polymerizes. I'm crying. No in this process.

By setting suitable conditions for gum production, gum is actively produced and removed. It is said that the rate-determining rate of NO gum production is the NO2 production stage (No+V'2o2-+Noz), and it is sufficient to provide a suitable temperature (about 80 DEG C.) and necessary residence time for the reaction. In addition, since the reaction reduces the number of molecules, it is advantageous for high-pressure gas reactions. Since the generated gum is suspended in the gas as fine particles, it is washed and removed with water or cleaning oil. The reactor for NO gum production may be a conventional cylindrical empty column. As a remover for the generated gummy particles, a packed column such as a Raschig ring is suitable for removing particles.

The coke oven gas from which the cam matter has been removed and whose temperature has been lowered by contact with the wash water then enters the dearomatization step (3). In the dealomatization step, aromatic components such as BTX and tar in coke oven gas are efficiently removed by absorbing oil such as creosote oil using high pressure.

When impurities in a gas are absorbed and removed using a solvent, the higher the operating pressure is, the more advantageous it is in terms of equilibrium.The higher the operating pressure, the lower the concentration of impurities in the gas leaving the absorption tower. Since the partial pressure is high, the driving force for mass transfer is also large, which has the advantage of facilitating absorption operations. The structure of the absorption tower may be a tray tower, but preferably a packed tower with a large contact area. The absorbed oil leaving the absorption tower is regenerated by steam stripping or other means in a separately provided regeneration tower and recycled for use. The purification of coke oven gas in the aforementioned steel mills is generally carried out at atmospheric pressure, but since the pressure in this process is high, the concentration of aromatic components leaving the absorption tower is inversely proportional to the relationship of vapor-liquid equilibrium. It has the advantage of being able to lower the value, which is actually several minutes lower. Therefore, the operating pressure must be determined taking this point into consideration. The gas leaving the dearomatization step then enters the hydrogenation step (4).

When oxygen gas is present in the coke oven gas, it is difficult to adsorb the oxygen component selectively over hydrogen gas, depending on the M absorbent of the currently industrialized molecular sheep method.

Therefore, it is necessary to remove the oxygen component in advance. A known method for removing oxygen is to perform hydrogenation in the presence of a catalyst and remove it as water. Conventionally, noble metal catalysts such as platinum and palladium are known as hydrogenation catalysts for oxygen, but these catalysts are not suitable for cases containing sulfur compounds such as coke oven gas because they are poisoned by sulfur and their activity decreases. do not have. In the present invention, as a result of examining various catalysts, it was found that nickel-molybdenum catalysts, which have conventionally been mainly used for hydrodesulfurization, are sometimes superior. Coke oven scum containing several tens of P P m of sulfurized t↑r1 such as hydrogen sulfide was tested using this catalyst, but even after about 4 months, there was no decrease in the activity of the deoxidizing hydrogenation reaction, and coke Carbon monoxide and carbon dioxide contained in the furnace gas coexist with hydrogen gas and methanation reaction (CO+3H2→C
H, +H20゜CO2+4H2→CH4+2H,,O)
There was no phenomenon of abnormal heat generation. The reason for this is not clear, but it is presumed that the sulfidation of the nickel-molybdenum catalyst increases the activity for the hydrogenation reaction, while conversely the activity for the methanation reaction is suppressed.

The reaction temperature shows activity even at relatively low temperatures, and a reactor inlet temperature in the range of 150 to 250°C is sufficient. However, the reactor outlet temperature rises due to the heat of hydrogenation reaction of oxygen and some olefins, and may reach around 4000C depending on the concentration of 02 and the like. The structure of the reactor may be a normal cylindrical drum type and no special structure is required. However, since the temperature of the gas at the reactor outlet becomes considerably high as mentioned above, it is thermoeconomically advantageous to provide a heat exchanger and preheat the reactor inlet gas to the required temperature using the high temperature gas exiting the reactor.

In addition to removing oxygen, the hydrogenation process described above also removes olefin hydrocarbons and organic sulfur compounds, which are present in coke oven gas in small amounts. Converting to hydrocarbons has the advantage of reducing the load on the molecular sheep process. The coarse furnace gas leaving the hydrogenation step then enters the molecular sheep step. In the molecular sheep process, methane, carbon oxide, carbon dioxide, and other impurities in the coke oven gas are selectively adsorbed and removed by various adsorbents, preferably under a pressure of 9 atmospheres or higher, and hydrogen gas is removed by the adsorbents. Pass through the layers. There are multiple tanks filled with adsorbent, and while one tank is in the process of adsorption, another tank is being regenerated under reduced pressure, and the other tank is used to store the product after regeneration in preparation for Ounce Dream. Piping various things such as pressurizing with hydrogen gas,
The system is designed to operate cyclically using switching valves and control instruments. The purity of the product hydrogen gas leaving this molecular sheep process can range from 99% to 99.999%, depending on the composition of the raw coke oven gas. In addition to impurities such as methane and carbon oxide, the purge gas produced as a by-product from the molecular sheep process also contains hydrogen gas due to adsorption tank switching operations, regeneration operations, etc., resulting in a recovery loss. Available for

As explained above, according to the present invention, harmful components and impurities in coke oven Jj gas can be efficiently removed and high-purity hydrogen gas can be produced, which is extremely effective in the chemical industry.

EXAMPLE When coke oven gas was treated using the apparatus shown in FIG. 1, the following results were obtained.

Hydrogen 552v% 55.2Vchi 534
v% 999 oxygen l, Q tt
l, Q tt --carbon monoxide 76t
t 7,5 n 8. l // -carbonate scum 2.0 // 2.0 /l 2.1 t
t-nitrogen 4.2 tt 4
．． 2 tt 4.5 tt O, 1 me
Tan 27. OII 27.0
1/28.7/l -C2)
! 4/C'2H62 start//, 2. 'll//
Fufu9〃 -Cs Ha/Cs Ha O,3
A-1/ 0.3/lt -10,3tt
-B'I'X minute 5o#"10iVN101VN'Y
-Heavy aromatic content 200 tt-11 Note 1) A commercially available nickel-molybdenum catalyst was used as the catalyst in the hydrogenation step.

2) The pressure distribution of the system was 15 atm after pressurization and 14 atm during the molecular sheep process.

3) Hydrogen sulfide and organic sulfur compounds were contained in the hydrogenation tower inlet gas at approximately 130 mg/Nm", but 100 um"
No residual oxygen was detected at the outlet of the hydrogenation tower even after several hours of operation.

[Brief explanation of the drawing]

The drawing is a system diagram showing one embodiment of the present invention. 1... Pressure increase process, 2... Degassing process, 3... Dearomatization process, 4... Hydrogenation process, 5... Mo I / Curar Sheep process, F... Raw material coke oven Gas, P...product hydrogen scum, W...purge gas. Patent applicant Kansai Thermal Chemical Co., Ltd. Mitsubishi Kakoki Co., Ltd. Representative Patent Attorney Yoshio Kimura S CL - 13-

Claims (2)

[Claims] (1) = l -xF In a method for producing high-purity hydrogen gas using the Cascara molecular sheep method,
The process of increasing the pressure of coke oven gas to 8 atmospheres or more, after increasing the pressure,
A process of forming a gummy substance using the increase in gas temperature during pressure increase and washing and removing the gummy substance, a process of absorbing and removing aromatic components by absorbing oil, and a process of removing oxygen and olefins in the presence of a catalyst. 1. A method for purifying coke oven gas, characterized in that the steps of hydrogenating and removing compounds, etc., are combined in said order. (2) A method for purifying coke oven gas according to claim 1, which uses a nickel-molybdenum catalyst as a hydrogenation catalyst.